Over the last thirty years it has been a goal of various government agencies to develop uses for the desert plant jojoba (Simmondsia chinensis), especially the extract produced from the jojoba seeds. Due to the jojoba plant's ability to thrive in arid climatic conditions in coarse desert soils and it's life span which can extend up to 200 years, the plant was thought to be particularly useful for developing an agricultural industry in the underutilized lands of the American southwest.
The jojoba plant produces an abundance of seeds with an average yield for a mature plant of about 12 pounds (dry weight). Jojoba seeds contain about 50% by weight of a colorless, odorless liquid extract which is commonly referred to as "jojoba oil". The extract is chemically an unsaturated wax made up of non-glyceride esters having a narrow range of chemical composition. Waxes of this type are relatively rare. Another natural source for wax esters is spermaceti, a liquid wax produced from the head of the sperm whale. As the sperm whale is an endangered species and interstate sale of its oil was banned in 1973, it is not recognized as a particularly useful source for wax esters.
Jojoba extract is more than 97% wax esters. Each wax ester is derived from one molecule of a long-chain monoethylenic alcohol esterified with one long-chain monoethylenic fatty acid. The wax esters typically are comprised of carbon chains of 38 to 44 carbon atoms. Suprisingly, the wax ester components of jojoba extract have been found to exhibit superior fungicidal capabilities.
Powdery mildew is the common name applied to one of the most damaging and wide spread diseases in the agricultural and horticultural industry. Powdery mildew is a disease caused by species of several genera of fungus on a number of different host plants. The variety of horticultural and agricultural plants susceptible to powdery mildew disease is large. The disease is called "powdery mildew" because the appearance of the mycelial growth gives a powder like appearance on the surface of the host. The white powdery growth appears on infected leaves, stems, fruit and flower buds. Infected leaves may also appear distorted and fall from the plant. Powdery mildew spores are easily spread by wind to nearby plant tissue and to other plants, resulting in an epidemic if left unchecked.
Various chemical compounds have been disclosed which claim suitability for use as a fungicide for controlling powdery mildew infection. For example, U.S. Pat. No. 5,366,995 discloses the use of short chain fatty acids and their salts as a fungicidal agent. The disclosed fatty acids generally have carbon chains of between 7 to 20 atoms and preferably at 18 carbons. The prior art does not disclose use of the high molecular weight wax esters commonly found in jojoba extract as a fungicidal agent.
Jojoba extract has been reported as a pretreatment to prevent powdery mildew infection on grape plants (Canadian Patent Application No. 2,103,014). Jojoba extract was previously thought to have limited commercial application. The mechanism of control was thought to be as a physical barrier similar to horticultural oils which have been known for many years. In our studies, it has been surprisingly determined that the wax esters found in jojoba extract are not merely an inert physical barrier but also a broad spectrum fungicide. This discovery gives rise to commercially important applications.
In modem agriculture and horticulture the avoidance of unnecessary environmental loading is a key commercial advantage. Both horticulture oils and fungicides are applied repeatedly during the early stages of the growing season to prevent the powdery mildew infection from becoming established. The oils and fungicides are applied multiple times per growth cycle to prevent powdery mildew infection and then again if powdery mildew appears. Since many crops have two or more growing cycles per year, this leads to yet more fungicidal treatments. As a result, the frequent fungicidal applications lead to a build up of that particular chemical agent in the environment (environmental loading). Conversely, application of the wax esters of the subject invention can be limited to instances where a powdery mildew infection occurs. Thus, wax ester fungicidal treatments are limited to a few, if any, application per growing season and environmental loading is significantly lowered. Less fungicidal applications result in a lower cost to growers.
In addition, the wax ester fingicidal agent is rainfast after the application has dried. Thus, the wax ester fungicidal agent kills existing infections and then prevents further infection over time. Jojoba extract has the ability to eradicate fungicidal tolerant or resistant powdery mildew strains that have evolved under current fingicidal protocols. Therefore, use of a jojoba extract as a fungicide is economically efficient and significantly reduces environmental loading.
The wax esters provide a greater degree of safety than horticultural oils and fungicides. Many of the existing horticultural oils and fungicides are generally not environmentally safe in their application. For example, use of petroleum oils and sulfuric fingicidal applications for powdery mildew are restrained under the federal regulations as they have serious environmental ramifications if applied in a concentrated form or in high volume. Further, the fungicides and oils are generally volatile. Thus, use of these materials is hazardous to workers applying the chemical. Another popular fungicide, sterol inhibitors, are also heavily regulated because of their environmental impact and the residues they leave on edible crops. The wax esters used in this invention provide particular stability and are significantly less volatile than horticultural oils. Specifically, the greater degree of unsaturation and the long carbon chains, which are almost twice as long as fatty acid oils, enhances stability and non-volatility. Jojoba extract is a safe and natural application and is not heavily impacted by regulatory laws.
Additionally the wax esters of the subject invention have other advantages which make them a particularly effective as a fungicidal agent. For example, the long chained wax esters are generally non-toxic for predator, beneficials and honeybees. The wax ester agent is generally non-phytotoxic at the preferred range of use and, unlike many of the prior art fungicides mentioned above, never "bum" plant tissue. In fact the wax esters have been found to promote photosynthesis and stomatal conductance in the host plant.